Chapter 9 Steering Systems 171
This design allows the steering shaft to collapse when
the vehicle is in a collision. For this reason it is called a
collapsible shaft. Collapsible shafts are often referred to as
telescoping shafts, since the shaft length is reduced as one
section of the shaft slides into the other in the same way a
portable telescope is collapsed.
During normal driving, the two halves of the steering
shaft are held in position by shear pins. Shear pins are
purposely made of a relatively weak material, usually
plastic. Their purpose is to break when sufficient pressure
is placed on them, preventing injury to the driver. If a
collision occurs that is severe enough to cause the driver to
strike the steering wheel, the shear pins break, allowing the
shaft to collapse.
Steering Couplers
A flexible steering coupler is installed at the bottom of
the steering shaft, just before the steering gear. This coupler
allows for slight variations in the alignment between the
shaft and steering gear. It also absorbs vibrations. The
disc coupler is usually a flexible rubber disc, as shown in
Figure 9-7. The steering shaft contains a yoke that is
connected to the disc at two points opposite each other
(180° apart). Another yoke is connected to the disc at 90°
from the shaft connection. This yoke is attached to the stub
shaft that leads into the steering gear, or it may be attached
to an intermediate steering shaft. The rubber disc transmits
turning effort while absorbing small vibrations from the
other parts of the steering system. The yokes are designed
to provide a connection if the flexible coupling breaks.
Some vehicles with one or more universal joints do not use
a steering coupler.
Steering Universals
On many newer cars, there is not enough clearance to
allow the steering shaft to make a straight connection with
the steering gear. Therefore, the upper and lower shafts
must be offset through the use of universal joints. Steering
shaft universal joints allow the shaft to turn through an
angle. Universal joints consist of a center cross that
connects two yokes. Each yoke is connected to one part of
the steering shaft. The yokes can twist as they rotate. This
allows the centerline of the steering shaft to change.
Figure 9-8 shows a typical universal joint installed on a
steering shaft.
Figure 9-6. A two-piece steering shaft assembly. (General Motors)
Attaching yoke
(to upper
steering shaft)
Cross
strap
Flexible
coupler
Cross strap
Yoke
Lower steering shaft
Figure 9-7. A flexible rubber steering coupler. (General Motors)
Coupling shield
Flexible
coupling
Bolt
Lower
intermediate
shaft
Seal Spring
Nut
Joint
coupling
Bolt
Upper intermediate
shaft